13. CORRELATION BETWEEN ANEUPLOIDY, MOSAICISM AND MORPHOKINETIC DEVELOPMENT IN 1550 BIOPSIED BLASTOCYSTS.

Despite the high number of recent studies, conflicting data are reported, and there is still considerable disagreement regarding which morphokinetic parameters are useful to predict blastocyst formation, implantation potential and ploidy status of the embryo. The first attempt to develop a model predicting embryo implantation used the time of division to 5 cells, the time between division from 3 to 4 cells and the time between division from 2 to 3 cells (Meseguer et al., 2011). More recently, the aneuploidy status of embryos was related to the start of blastulation and the formation of a full blastocyst. The aneuploidy risk classification built proved beneficial in a correlation with live birth when applied to non-biopsied embryos (Campbell et al., 2013). This retrospective study was based on 1550 blastocysts which were subjected to preimplantation genetic testing for aneuploidy (PGT-A) between August 2011 and December 2018 in Istanbul Memorial Hospital (n=659 euploids; n=831 aneuploids; n=60 mosaics). Incubation was performed in time-lapse incubators (EmbryoScope™). All relevant events (fertilization, cleavages, morula and blastocyst formation) were checked daily, and time of cleavage to two-cell embryo (t2) and subsequent divisions t3, t4, t5, t6, t7, t8, t9+, tM, tSB, tB and tEB were recorded in the EmbryoViewer® workstation. PGT-A was done by NGS ReproSeq on Ion Torrent S5 (Thermo Fisher Scientific) or aCGH (Illumina) following trophectoderm biopsy. Mann-Whitney U and Kruskal Wallis tests were used in this study. When euploid embryos were compared with aneuploids, the time to reach the blastocyst stage was 3 hours earlier in euploids (tB=104.60h vs. 107.64h; p<0.0001). Interestingly, euploids and mosaics were found to have a similar morphokinetic behavior; for example, t2 was 25.6h in euploids and mosaics, and 26.3h in aneuploids (p=0.006). Aneuploids were then subdivided into five groups: 2-chromosome aneuploidies, complex aneuploidies, monosomies, trisomies and partial aneuploidies. The sub-analysis done for the time of the first cleavage t2 was statistically significant (p=0.021) and showed that euploids were different from 2-chromosome aneuploids and from complex aneuploids; complex aneuploids were different from mosaics which were different from partial aneuploids; two-chromosome aneuploids were different from mosaics and from trisomies. A second subgroup analysis was done for the time to achieve the 8-cell stage (t8) and showed that euploids are statistically significantly different from all aneuploid subcategories but not from mosaics (p=0.0017). The mosaic embryos' morphokinetic parameters were similar with the euploid blastocysts. Observed time-lapse differences between euploid and aneuploid blastocysts suggests that the embryos are being affected by the chromosomal constitution throughout the embryo development. Even though the variances at the initial cleavages are as short as half an hour, this increases to a three hour at the blastocyst stage. The study presented above can be used to prioritize the embryos according to the morphokinetic variables to biopsy and diagnose the embryos with highest chance of being euploid thus reducing the costs especially for couples who have more than one blastocyst. [ABSTRACT FROM AUTHOR]